1. Field of the Invention
This invention relates to a blade shape creation program and method for creating the blade shape of a cooling fan.
2. Description of the Related Art
When the blade shape of a cooling fan installed in a vehicle is to be created (drawn) in designing the cooling fan, for example, the first step is to create (draw) the cross-sectional shapes of a blade at a plurality of locations in the hub diameter direction of the blade. Then, based on these cross-sectional shapes of the blade, the entire shape of the blade (visible outline and exterior surface) is created (drawn) by spline interpolation or the like. In drawing the cross-sectional shape of the blade, “average camber curve (camber line)”, which is a basic skeleton of the cross-sectional shape of the blade, is drawn. A method using “Joukowski airfoil” shown, for example, in the following document is named as one of ordinary methods for drawing the camber line:                T. Fujimoto, “2nd Revision of Fluid Dynamics”, 2nd Revision, 6th Edition, YOKENDO Co., Ltd., published Jan. 20, 1992, p. 141”        
An outline of this method will be described with reference to FIGS. 10(a) and 10(b). A combination of two circles 1 and 2 with centers M and M′, as shown in FIG. 10(a) , is transformed into coordinates (mapped) by the equation (1) offered below. An airfoil (cross-sectional shape of blade) 3 as shown in FIG. 10(b), which is obtained by this coordinate transformation (mapping), is the “Joukowski airfoil”. A centerline of this airfoil (cross-sectional shape of blade) 3 is a camber line 4. To change the airfoil profile (camber line), the shapes of the two circles 1 and 2 before coordinate transformation are adjusted.
                              z          =                      ζ            +                                          a                2                            ζ                                      ,                  a          =                      c            4                                              (        1        )            
To improve the performance of the blade (lift performance and drag performance), it is necessary to change (adjust) the shape of the camber line and study influence on the performance of the blade. For this purpose, it is effective to individually change (adjust) a plurality of design factors (details to be described later), which determine the shape of the camber line, thereby directly investigating the degree of contribution of each design factor to the performance of the blade. Particularly, the ability to change each design factor, independently of each other, on the leading edge side of the maximum camber point of the camber line (see FIG. 3, details to be described later) and on the trailing edge side of the maximum camber point would be very effective for studying the performance of the blade.
However, conventional methods, such as the method using “Joukowski airfoil”, pose difficulty in changing each design factor independently. Needless to say, changing each design factor, independently on the leading edge side and the trailing edge side of the camber line, is also difficult.
The present invention has been accomplished in light of the above-described circumstances. It is an object of the present invention to provide a blade shape creation program and method capable of changing a plurality of design factors, which determine the shape of a camber line, on the leading edge side and the trailing edge side of the camber line, with the leading edge side and the trailing edge side being separated from each other, in changing (adjusting) the shape of the camber line.
It is another object of the present invention to provide a blade shape creation program and method capable of reliably checking the created camber line shape based on numerical values, without relying on visual checks.